linux-kernel - Re: [PATCH v2 06/14] locks: don't walk inode->i_flock list in locks

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Message-ID: <51BC826B.5060805@samba.org>
Date:	Sat, 15 Jun 2013 11:04:11 -0400
From:	Simo <idra@...ba.org>
To:	Jeff Layton <jlayton@...hat.com>
CC:	viro@...iv.linux.org.uk, matthew@....cx, dhowells@...hat.com,
	sage@...tank.com, smfrench@...il.com, swhiteho@...hat.com,
	Trond.Myklebust@...app.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-afs@...ts.infradead.org,
	ceph-devel@...r.kernel.org, linux-cifs@...r.kernel.org,
	samba-technical@...ts.samba.org, cluster-devel@...hat.com,
	linux-nfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	piastryyy@...il.com
Subject: Re: [PATCH v2 06/14] locks: don't walk inode->i_flock list in locks_show

On 06/15/2013 07:05 AM, Jeff Layton wrote:
> On Fri, 14 Jun 2013 07:52:44 -0400
> Simo <idra@...ba.org> wrote:
>
>> On 06/13/2013 04:26 PM, Jeff Layton wrote:
>>> The only real solution I can think of is to put flock locks into the
>>> blocked_list/blocked_hash too, or maybe giving them a simple hlist to
>>> sit on.
>>>
>>> I'll fix that up in the next iteration. It'll probably make flock()
>>> tests run slower, but such is the cost of preserving this procfile...
>> How hard would it be to make the procfile stuff optional ?
>> So that those that need performance can decide to not use it ?
>> Maybe even something that can be disabled at run time ? Not just compile
>> time.
>>
> (re-adding back the cc lists...)
>
> It'd be tricky, especially if you want to do it at runtime. The
> procfile itself is not a problem per-se. The real problem is the
> tracking you have to do in order to eventually present the procfile. So
> a boot-time or compile-time switch might be reasonable, but a runtime
> switch will probably never really be.

Just to be clear, I meant for a switch to turn it off at runtime, I 
understand very well that it would be way too hard to turn on at 
runtime. But killing the perf problem might be desirable on a system you 
cannot just reboot.

> I have a new patchset that I'm testing now though that should address
> Bruce's concerns about iterating over that global list. So far, it
> seems to be at least as fast as the latest patchset I posted.
>
> It makes the (spin)locking a bit more complex, but hopefully I can
> document this well enough that it's not a great concern.
>
> Stay tuned...

Thanks Jeff,
this is very valuable work.

Simo.

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